1. Field of the Invention
The present invention relates to a tube coupling for connecting tubes.
2. Description of the Related Art
Conventionally known tube couplings are disclosed in the Official Gazette of the Japanese Laid-Open Publication Application No.Hei8-326976, for example. As shown in FIG. 6 and FIG. 7, a conventional tube coupling comprises a coupling body 10, a separation prevention ring 20 which is disposed within the coupling body 10, and a release ring 30 which pushes the separation prevention ring 20 while moving in a predetermined range from the coupling body 10.
The separation prevention ring 20 is intervened between a back ring 13 and a guide ring 14, which are disposed within the coupling body 10 so to be prevented from separating from the coupling body 10. A seal ring 40 is disposed in the coupling body 10 to make sealing secure by tightly adhering to the outside wall of the tube body 1. And, a shoulder portion 11, which an inside end portion of the tube body 1 contacts, is formed in the coupling body 10.
As shown in FIG. 6 and FIG. 7, the separation prevention ring 20 has outer edges 22 that intervene between the back ring 13 and the guide ring 14 and inner edges 21 which bites into the tube body 1 and has a zigzagged annular shape which is of many radial grooves 23 alternately formed by the inner edges 21 and the outer edges 22.
The outer peripheral edges of the separation prevention ring 20, namely the outer edges 22, have a fixed width and substantially the same total length as that of the inner edges 21. When the tube body 1 is inserted into the separation prevention ring 20, the inner edges 21 bite into the outer wall of the tube body 1 to prevent the tube body 1 from falling out of the coupling body 10.
But, in the separation prevention ring 20 shown in FIG. 7, since the total length of the outer edges 22 fixed by the back ring 13 and the guide ring 14 is substantially the same as that of the inner edges 21 which bite into the tube body 1, if the tube body 1 fixed by the inner edges 21 is forcedly pulled, a force applied to the outer edges 22 deforms the original shape of the outer edges 22 and damages the outer edges 22. Accordingly, the separation prevention ring 20 is separated from the back ring 13 and the guide ring 14 and may be separated from the tube coupling 10 as a result.
Since it is configured so that a large number of inner edges 21 bite into the tube body 1 at the same time, when the tube body 1 is slantly pulled from the coupling body 10, a part of the inner edges 21 can no longer properly bite into the outer wall of the tube body 1, causing the tube body 1 to fall out of the coupling body 10.